The present invention relates to a fluid machine served as an expansion device and a compression device.
It has been proposed that a refrigerant compression device in an air-conditioning cycle is utilized as an expansion device to perform a Rankine cycle (refer to Japanese Unexamined Patent Publication No. 6-159013). The structure of a fluid machine served as an expansion device and a compression device is not described in detail in Japanese Unexamined Patent Publication No. 6-159013. However, it is easy to assume that a scroll type fluid machine disclosed in Japanese Unexamined Patent Publication No. 5-296163 can be utilized as the fluid machine served as the expansion device and the compression device.
When the above scroll type fluid machine functions as the compression device, an operation chamber defined by movable and fixed scroll members is moved from an outer peripheral side to a central side while reducing in volume by the orbital movement of the movable scroll member relative to the fixed scroll member. Thus, refrigerant gas is compressed in the operation chamber. The high pressure refrigerant gas in the operation chamber at the central side is discharged to the high pressure chamber via a port formed in the fixed scroll member and then flows out from the high pressure chamber to an external circuit.
When the above scroll type fluid machine functions as the expansion device, the high-pressure refrigerant gas introduced from the external circuit into the high pressure chamber is introduced into the operation chamber at the central side via the port. Then, the operation chamber at the central side is moved to the outer peripheral side while increasing in volume by expansion of the refrigerant gas. Thus, the movable scroll member orbits relative to the fixed scroll members so that driving power is generated.
When the above scroll type fluid machine functions either as the compression device and the expansion device, the refrigerant gas flows between the operation chamber at the central side and the high pressure chamber via the common port.
The port regularly communicates with the high pressure chamber in the above fluid machine. Thus, when the above fluid machine functions as the compression device, at the timing when the compressed refrigerant gas in the operation chamber at the central side is discharged into the high pressure chamber, the operation chamber communicates with the port. Namely, the timing is always constant.
However, an appropriate timing when the refrigerant gas in the operation chamber at the central side is discharged into the high pressure chamber varies in accordance with an operational state of the compression device such as a rotational speed (an orbital speed of the movable scroll member) and suction pressure. Thus, in the structure in which the compressed refrigerant gas is discharged from the operation chamber into the high pressure chamber at the constant timing, the refrigerant gas is not compressed to a predetermined pressure when the suction pressure is low. Therefore, there arises a problem that the refrigerant gas flows back from the high pressure chamber to the operation chamber and efficiency is lowered.
To solve such problem, a discharge valve is provided for opening and closing the port in the fluid machine that functions only as the compression device. The discharge valve is served as a differential pressure regulating valve (e.g. a reed valve) that opens and closes the port in accordance with the pressure difference between the pressure in the operation chamber acting in the direction to open the port and the pressure in the high pressure chamber acting in the direction to close the port.
However, when the discharge valve served as the differential pressure regulating valve is utilized in the fluid machine served as the compression device and the expansion device, the discharge valve blocks the flow of the refrigerant gas from the high pressure chamber to the operation chamber upon functioning as the expansion device. Thus, there arises a problem that the fluid machine actually does not function as the expansion device. Also, there similarly arises such problem in other type machines such as vane type and piston type machines in addition to the scroll type machine.